Various endoscopes (which shall be called electronic endoscopes in the present invention) wherein such solid state imaging devices as charged coupled devices (CCD's) are used for imaging means have been recently suggested.
Such electronic endoscope has advantages that the resolving degree is higher than in a fiberscope, the recording and reproduction of picture images are easy and such picture image processes as the magnification of picture images and comparison of two picture surfaces are easy.
With the above mentioned endoscope, a body cavity interior or the like can be observed by inserting the insertable part of a fine diameter into the body cavity or a curing treatment can be made with a treating tool. Therefore, in order to reduce a pain to the patient when the insertable part is inserted, it is desirable to make the tip of the above mentioned insertable part fine. In order to meet such desire, in the specification of U.S. Pat. No. 4,622,954, there is disclosed a technique wherein a solid state imaging device is arranged in parellel with the lengthwise direction of an insertable part so that such other components as, for example, a forceps channel, light guide and air and water feeding tube may be effectively arranged and the outside diameter of the insertable part may be made small.
It is also desirable that the tip of the insertable part is in such form easy to insert into a body cavity as, for example, a tapered form but the form of this tip is restricted by the sizes and arrangements of components provided within this tip.
In the above mentioned electronic endoscope, such components as not only an imaging means having an objective system as an image forming optical system and a solid state imaging device but also a forceps channel, air and water feeding tube and light guide are generally internally provided in the above mentioned tip. In comparing the sizes in the cross-section of the above mentioned respective components including the above mentioned solid state imaging device, it is found that generally the above mentioned solid state imaging device is the largest, to be followed by the forceps channel and light guide in the order mentioned. By the way, in case the observing performance is particularly considered to be more important than the processing perfromance, the sizes will be in the order of the solid state imaging device, light guide and forceps channel.
Now, it is considered that the tip will be able to be made the finest if the above mentioned solid state imaging device and the second largest component (generally the forceps channel) next to this solid state imaging device are arranged adjacently to each other. Also, in case the above mentioned solid state imaging device is, for example, square, the tip will be able to be made fine to some extent by arranging the above mentioned second largest component on the side of this solid state imaging device.
Further, in order to make small the outside diameter of the tip on the tip side beyond the above mentioned solid imaging device, the objective system and the second largest component, for example, the forceps channel may be set to be close to each other.
Now, conventionally, in the above mentioned solid state imaging device, a chip on which many light receiving elements (picture elements) are arranged is arranged in the central part and is electrically connected with leads provided in a package through bonding wires or the like. Therefore, the entire solid state imaging device is larger than the size of the image area of the above mentioned chip. Also, generally, the outside diameter of the above mentioned solid state imaging device is larger than that of the objective system.
As mentioned above, conventionally, the position of the above mentioned objective system has been restricted by the size of the above mentioned solid state imaging device and it has not been considered to arrange the above mentioned objective system and the second largest component to be close to each other so that the outside diameter of the tip on the tip side beyond the solid state imaging device may be made smaller and the tip may be in the form easy to insert into a body cavity.